package redis_pool

import (
	"bytes"
	"crypto/rand"
	"crypto/sha1"
	"errors"
	"fmt"
	"io"
	"strconv"
	"sync"
	"time"

	"git.loafle.net/commons_go/redis_pool/internal"
	"github.com/garyburd/redigo/redis"
)

var nowFunc = time.Now // for testing

var (
	// ErrPoolExhausted is returned from a pool connection method (Do, Send,
	// Receive, Flush, Err) when the maximum number of database connections in the
	// pool has been reached.
	ErrPoolFull = errors.New("Redis pool: Pool is reached maximum capacity.")
)

var (
	errPoolClosed = errors.New("Redis pool: connection pool closed")
	errConnClosed = errors.New("Redis pool: connection closed")
)

// Pool maintains a pool of connections. The application calls the Get method
// to get a connection from the pool and the connection's Close method to
// return the connection's resources to the pool.
//
// The following example shows how to use a pool in a web application. The
// application creates a pool at application startup and makes it available to
// request handlers using a package level variable. The pool configuration used
// here is an example, not a recommendation.
//
//  func newPool(addr string) *redis.Pool {
//    return &redis.Pool{
//      MaxIdle: 3,
//      IdleTimeout: 240 * time.Second,
//      Dial: func () (redis.Conn, error) { return redis.Dial("tcp", addr) },
//    }
//  }
//
//  var (
//    pool *redis.Pool
//    redisServer = flag.String("redisServer", ":6379", "")
//  )
//
//  func main() {
//    flag.Parse()
//    pool = newPool(*redisServer)
//    ...
//  }
//
// A request handler gets a connection from the pool and closes the connection
// when the handler is done:
//
//  func serveHome(w http.ResponseWriter, r *http.Request) {
//      conn := pool.Get()
//      defer conn.Close()
//      ...
//  }
//
// Use the Dial function to authenticate connections with the AUTH command or
// select a database with the SELECT command:
//
//  pool := &redis.Pool{
//    // Other pool configuration not shown in this example.
//    Dial: func () (redis.Conn, error) {
//      c, err := redis.Dial("tcp", server)
//      if err != nil {
//        return nil, err
//      }
//      if _, err := c.Do("AUTH", password); err != nil {
//        c.Close()
//        return nil, err
//      }
//      if _, err := c.Do("SELECT", db); err != nil {
//        c.Close()
//        return nil, err
//      }
//      return c, nil
//    }
//  }
//
// Use the TestOnBorrow function to check the health of an idle connection
// before the connection is returned to the application. This example PINGs
// connections that have been idle more than a minute:
//
//  pool := &redis.Pool{
//    // Other pool configuration not shown in this example.
//    TestOnBorrow: func(c redis.Conn, t time.Time) error {
//      if time.Since(t) < time.Minute {
//        return nil
//      }
//      _, err := c.Do("PING")
//      return err
//    },
//  }
//
type Pool interface {
	Start() error
	Stop()

	Get() redis.Conn
	Put(conn redis.Conn)

	Capacity() int
	Available() int
}

type pool struct {
	ph PoolHandler

	connections         map[redis.Conn]*pooledConnection
	connectionQueueChan chan *pooledConnection

	stopChan chan struct{}
	stopWg   sync.WaitGroup
}

type idleConn struct {
	c redis.Conn
	t time.Time
}

// NewPool creates a new pool.
//
// Deprecated: Initialize the Pool directory as shown in the example.
func New(ph PoolHandler) Pool {
	p := &pool{
		ph: ph,
	}
	return p
}

func (p *pool) Start() error {
	if nil == p.ph {
		panic("GRPC Pool: pool handler must be specified.")
	}
	p.ph.Validate()

	if p.stopChan != nil {
		return fmt.Errorf("GRPC Pool: pool is already running. Stop it before starting it again")
	}
	p.stopChan = make(chan struct{})
	p.connections = make(map[redis.Conn]*pooledConnection, p.ph.GetMaxCapacity())
	p.connectionQueueChan = make(chan *pooledConnection, p.ph.GetMaxCapacity())

	if 0 < p.ph.GetMaxIdle() {
		for i := 0; i < p.ph.GetMaxIdle(); i++ {
			if err := p.createConnection(); nil != err {
				p.Stop()
				return err
			}
		}
	}

	return nil
}

func (p *pool) Stop() {
	if p.stopChan == nil {
		panic("GRPC Pool: pool must be started before stopping it")
	}
	close(p.connectionQueueChan)

	for k, _ := range p.connections {
		p.destroyConnection(k)
	}

	p.stopWg.Wait()
	p.stopChan = nil
}

func (p *pool) createConnection() error {
	maxCapacity := p.ph.GetMaxCapacity()
	currentConnectionCount := len(p.connections)
	if currentConnectionCount >= maxCapacity {
		return ErrPoolFull
	}

	conn, err := p.ph.Dial()
	if err != nil {
		return err
	}
	pc := &pooledConnection{
		p:        p,
		c:        conn,
		idleTime: time.Now(),
		inUse:    false,
	}
	p.connections[conn] = pc
	p.connectionQueueChan <- pc
	p.stopWg.Add(1)

	return nil
}

func (p *pool) destroyConnection(conn redis.Conn) error {
	var err error
	pc, ok := p.connections[conn]
	if !ok {
		return nil
	}
	err = pc.c.Close()
	if nil != err {
		return err
	}
	delete(p.connections, conn)
	p.stopWg.Done()

	return nil
}

func (p *pool) get() (*pooledConnection, error) {
	var pc *pooledConnection
	var err error

	avail := len(p.connectionQueueChan)
	if 0 == avail {
		if err = p.createConnection(); nil != err {
			return nil, err
		}
	}

	for {
		select {
		case pc = <-p.connectionQueueChan:
			// All good
		default:
		}
		idleTimeout := p.ph.GetIdleTimeout()
		if 1 < len(p.connectionQueueChan) && 0 < idleTimeout && pc.idleTime.Add(idleTimeout).Before(time.Now()) {
			go p.destroyConnection(pc.c)
			continue
		}
		break
	}

	return pc, nil
}

func (p *pool) Get() redis.Conn {
	var err error
	var pc *pooledConnection
	if pc, err = p.get(); nil != err {
		return errorConnection{err}
	}

	pc.inUse = true

	return pc
}

func (p *pool) Put(conn redis.Conn) {
	pc, ok := p.connections[conn.(*pooledConnection).c]
	if !ok {
		return
	}

	pc.idleTime = time.Now()
	pc.inUse = false

	select {
	case p.connectionQueueChan <- pc:
		// All good
	default:
		// channel is full
		return
	}
}

func (p *pool) Capacity() int {
	return cap(p.connectionQueueChan)
}

func (p *pool) Available() int {
	return len(p.connectionQueueChan)
}

type pooledConnection struct {
	p        *pool
	c        redis.Conn
	idleTime time.Time
	inUse    bool
	state    int
}

var (
	sentinel     []byte
	sentinelOnce sync.Once
)

func initSentinel() {
	p := make([]byte, 64)
	if _, err := rand.Read(p); err == nil {
		sentinel = p
	} else {
		h := sha1.New()
		io.WriteString(h, "Oops, rand failed. Use time instead.")
		io.WriteString(h, strconv.FormatInt(time.Now().UnixNano(), 10))
		sentinel = h.Sum(nil)
	}
}

func (pc *pooledConnection) Close() error {
	c := pc.c
	if _, ok := c.(errorConnection); ok {
		return nil
	}
	pc.c = errorConnection{errConnClosed}

	if pc.state&internal.MultiState != 0 {
		c.Send("DISCARD")
		pc.state &^= (internal.MultiState | internal.WatchState)
	} else if pc.state&internal.WatchState != 0 {
		c.Send("UNWATCH")
		pc.state &^= internal.WatchState
	}
	if pc.state&internal.SubscribeState != 0 {
		c.Send("UNSUBSCRIBE")
		c.Send("PUNSUBSCRIBE")
		// To detect the end of the message stream, ask the server to echo
		// a sentinel value and read until we see that value.
		sentinelOnce.Do(initSentinel)
		c.Send("ECHO", sentinel)
		c.Flush()
		for {
			p, err := c.Receive()
			if err != nil {
				break
			}
			if p, ok := p.([]byte); ok && bytes.Equal(p, sentinel) {
				pc.state &^= internal.SubscribeState
				break
			}
		}
	}
	c.Do("")

	pc.p.Put(pc)

	return nil
}

func (pc *pooledConnection) Err() error {
	return pc.c.Err()
}

func (pc *pooledConnection) Do(commandName string, args ...interface{}) (reply interface{}, err error) {
	ci := internal.LookupCommandInfo(commandName)
	pc.state = (pc.state | ci.Set) &^ ci.Clear
	return pc.c.Do(commandName, args...)
}

func (pc *pooledConnection) Send(commandName string, args ...interface{}) error {
	ci := internal.LookupCommandInfo(commandName)
	pc.state = (pc.state | ci.Set) &^ ci.Clear
	return pc.c.Send(commandName, args...)
}

func (pc *pooledConnection) Flush() error {
	return pc.c.Flush()
}

func (pc *pooledConnection) Receive() (reply interface{}, err error) {
	return pc.c.Receive()
}

type errorConnection struct{ err error }

func (ec errorConnection) Do(string, ...interface{}) (interface{}, error) { return nil, ec.err }
func (ec errorConnection) Send(string, ...interface{}) error              { return ec.err }
func (ec errorConnection) Err() error                                     { return ec.err }
func (ec errorConnection) Close() error                                   { return ec.err }
func (ec errorConnection) Flush() error                                   { return ec.err }
func (ec errorConnection) Receive() (interface{}, error)                  { return nil, ec.err }